1. Field of the Invention
The present invention relates to the synthesis and use of salicylic acid diphosphates for use as flame retardant materials. More specifically, the materials are produced by the synthesis of methyl salicylate, POCl.sub.3 and either (a) bisphenol-A; (b) resorcinol; or (c) hydroquinone. The materials can be used to provide flame retardancy to any materials in which fire retardancy is desired, particularly to fibrous materials and plastics.
2. Technology Description
Although fiber materials composed of polyester-based synthetic fibers possess a variety of excellent physical and chemical properties, a common drawback is their tendency to combust, for which reason such polyester-based synthetic fiber materials have traditionally been subjected to finishing treatment for flame retardancy.
To impart flame retardancy to polyester-based synthetic fiber materials by finishing treatment as mentioned above, the prior art teaches the use of halogen compounds as flame retardant compounds, and flame retardancy has been imparted to polyester-based synthetic fiber materials by finishing treatment with such halogen compounds.
Here, bromine- and chlorine-containing compounds are known to be particularly effective as halogen compounds, and finishing treatment with these halogen compounds on polyester-based synthetic fiber materials typically involves dissolving a halogen-containing compound such as a halogenated cycloalkane, specifically hexabromocyclododecane, in a solvent, or using a dispersing agent or the like for its emulsification and dispersion in water, in combination with other additives when necessary, to prepare a treatment solution which is then applied to the polyester-based synthetic fiber materials mentioned above by a method such as coating, immersion or spraying.
However, when a halogen compound is applied to a polyester-based synthetic fiber material in this manner for flame retardancy, harmful halide gas is generated in the event of combustion of the polyester-based synthetic fibers, thus having an adverse effect on the environment, and therefore in recent years restrictions have been imposed on such halogen compounds.
In light of this, as alternative flame retardant compounds instead of the above-mentioned halogen compounds, the prior art has also employed phosphorus-containing compounds such as phosphoric esters and the like to impart flame retardancy to polyester-based synthetic fiber materials.
Here, the phosphorus-containing compounds which have traditionally been in common use as flame retardant compounds have low phosphorus contents and molecular weights usually as low as 200-400, and tend to degrade and volatilize at lower than the inflammation point of polyester-based synthetic fibers; consequently, they cannot impart flame retardancy to the polyester-based synthetic fiber materials as adequately as the above-mentioned halogen compounds, and thus such phosphorus compounds have had to be applied in large amounts in order to impart satisfactory flame retardancy to polyester-based synthetic fiber materials.
However, application of large amounts of these phosphorus compounds tends to cause trouble during the treatment, and when applied in large amounts phosphorus compounds result in an inferior hand of the polyester-based synthetic fiber materials.
Furthermore, when such phosphorus compounds are applied to polyester-based synthetic fiber materials, they gradually migrate through the surface of the polyester-based synthetic fiber materials with the passing of time, and their migration is accompanied by that of disperse dyes added for dyeing of the polyester-based synthetic fiber materials and dissolved in the phosphorus compounds, resulting in the problem known as "bleeding to surface" which lowers the color fastness.
U.S. Pat. No. 5,614,573 discloses a new class of materials proposed for use as fire retardants and are obtained by reacting phosphoryl compounds such as phosphorus oxychloride and phenylphosphonic dichloride, with salicylic acid derivatives, phthalic acid derivatives, dihydroxydiphenylsulfone derivatives or dihydroxydiphenylpropane derivatives. In the embodiment where the use of salicylic acid derivatives of phosphoryl compounds are suggested for use, the resulting composition is a monophosphate. To the extent necessary for completion of this disclosure, the contents of this patent is expressly incorporated by reference.
Despite the above teachings, there still exists a need in the art for improved fire retardant chemicals.